FIG. 1 is a plane view illustrating an ITO thin film for a capacitive touch screen, and FIG. 2 is a plane view illustrating an operating mechanism of conventional capacitive touch screen.
Referring to FIG. 1, a conventional touch screen electrically senses a contact position of a finger. When the finger which is a kind of conductive material, locates on an electrode, electric charges can gather between the electrode and the finger. If the electric charges gather, it is possible to measure capacitance between the finger and the electrode, so as to note the finger's touch indirectly.
Not to hide a liquid crystal display or another display, the electrodes of the touch screen may be formed of transparent conductive material, such as ITO (Indium Tin Oxide).
In (a) of FIG. 1, transparent electrode patterns vertically aligned (along y-axis) are provided. The vertically aligned transparent electrode patterns are provided on a transparent film 11 made of plastic sheet or glass, and they consist of first nod patterns 12 and first connecting patterns 13 which connect the first nod patterns 12 vertically.
In (b) of FIG. 1, other transparent electrode patterns horizontally aligned (along x-axis) are provided. The horizontally aligned transparent electrode patterns provided on another transparent film 14, consist of second nod patterns 15 and second connecting patterns 16 which connect the second nod patterns 15 horizontally.
Generally the conventional touch screen may be provided by overlaying the ITO transparent sheets of (a) and (b). One example of the overlaid structure of the two transparent sheets mutually bonded is illustrated in (c) of FIG. 1.
As shown, the second nod patterns 15 and the first nod patterns 12 are positioned alternately, such that the connecting patterns connecting the first or second nod patterns intersect up and down. These connecting patterns may be electrically separated by the transparent insulating sheet.
According to the touch screen structure of (c) of FIG. 1, a signal intense passing through the electrode patterns aligned vertically and horizontally may be changed in accordance with the finger's contact position, such that the coordinates can be calculated by using the changes of the signal intense.
In detail, after deciding the x- and y-coordinates using the signal intenses 23 and 24 of the electrode patterns, the coordinates of the intersecting position 25 may be the position of the fingers contact.
In this instance, electric signal may be generated by the change of the capacitance of the transparent electrode pattern at the fingers contact position 22, to be transmitted to a controller for deciding the coordinates of the contact point. The transparent electrode patterns made of ITO (Indium Tin Oxide) are conductive, but of having high resistance in comparison with general metal.
Since the signal loss by the resistance of the electrode pattern is proportional to area and length of the electrode pattern, manufacturers have a limit to enlarge the size of the touch screens.